What is a shutter?

To get the most out of this tutorial you really need a camera that allows manual control over shutter speed. Ideally this should be either full manual or shutter priority exposure, although some snapshot cameras do have an option for longer shutter speeds. Check your camera manual if you're not sure. A good solid tripod and some sort of remote shutter release will also be useful.

Having covered exposure and aperture control in previous tutorials, this month I'm going to take a look at the other main exposure control - shutter speed. As well as affecting exposure, shutter speed can also be adjusted to produce a number of other effects and is the most powerful tool for capturing motion in a still photograph.

All cameras, be they film or digital, have a shutter. In film cameras and digital SLRs this is simply a mechanical barrier that prevents light from falling on the film or sensor until it is needed. Digital compact cameras usually have an electronic "shutter". When a picture is taken, the shutter is opened for a precisely measured amount of time allowing light to pass through. The duration of the exposure is set by the camera's light meter, and depends on the amount of available light and the aperture setting.

Most digital cameras will have a range of available settings from a few seconds to a few thousandths of a second. Some can go as high as 1/4000th of a second, some can time a shutter release as long as 30 seconds and many also have a feature called a â€˜B' setting, in which the shutter stays open for as long as you hold the shutter release down. (The â€˜B' is from bulb; very old cameras commonly used an air-bulb attachment as a remote shutter release.) It's worth noting however that some older digital cameras suffer from increased image noise on very long exposures. If your camera has adjustable noise reduction, set it to maximum for long exposure shots.

Shutter priority mode (usually â€˜S' on the mode dial) is a semi-automatic exposure mode in which the photographer sets the desired shutter speed, and the camera's exposure system then sets the aperture accordingly to produce the correct exposure.

Most people usually let the camera set both the shutter speed and aperture automatically. Under normal daylight conditions, the shutter speed will usually be set to between 1/125th and 1/1000th of a second, since this is fast enough to freeze most movement and to reduce the effects of camera shake. However in low light conditions the camera may set a slower shutter speed, with an increased risk of movement blur and camera shake. Most cameras will display some sort of warning if this occurs.